Portable telephones based on W-CDMA scheme perform communications in PtM (Point to Multipoint) mode in which one network communicates with multiple portable telephones by using a common channel, and perform communications in PtP (Point to Point) mode in which one network communicates with one portable telephone by using a separate channel.
MBMS (Multimedia Broadcast Multicast Service) disclosed by Patent Document 1 (National Publication of International Patent Application No. 2005-525065) and Patent Document 2 (National Publication of International Patent Application No. 2005-536142) is defined in 3GPP Specification TS25.331 etc. and is a function of delivering multimedia data such as videos, images, and sound. For the delivery of user information by MBMS, PtM mode is basically to be employed in order to efficiently use of radio wave power; however, PtP mode may also be used.
Patent document 3 (Japanese Patent Laid-Open No. 2002-368684) discloses that when the error in receiving multicast data through a common channel (FACH) corresponding to PtM mode occurs successively for more than a predetermined number of times, a mobile station requests a base station to set a separate channel (DCH) corresponding to PtP mode for retransmission, and the base station sets a DCH for retransmission in response to the request of the mobile station to retransmit data to be retransmitted by using the DCH for retransmission and monitors the reception status thereafter to restart the reception through a common channel.
Patent Document 1: National Publication of International Patent Application No. 2005-525065.
Patent Document 2: National Publication of International Patent Application No. 2005-536142.
Patent Document 3: Japanese Patent Laid-Open No. 2002-368684.